Master cylinder for power and no-power actuation

ABSTRACT

A master cylinder assembly has a secondary piston assembly and a primary piston assembly mounted in a common bore to provide a primary pressurizing chamber between the piston assemblies and a secondary primary chamber between the secondary piston assembly and one end of the bore. The primary piston assembly is composed of two concentric pistons, one extending through a bore in the other. Two input members are provided, one of which is arranged to move both primary pistons concentrically under brake booster power to actuate the master cylinder, and the other of which is arranged to move only one of the primary pistons, without moving the other, to actuate the master cylinder manually when no power assist is available from the booster. The booster assembly is actuated through a manually moved push rod which in turn permits movement of a valve input member forming a part of the booster control valve assembly. The valve input member is arranged so that it normally follows movement of the push rod but is not positively attached thereto. A reaction system in the booster provides for booster &#39;&#39;&#39;&#39;feel&#39;&#39;&#39;&#39; to be transmitted to the input push rod. The booster control valve assembly is mounted in the booster power wall. The power wall includes one or more power diaphragms and is actuated by differential pressures imposed on opposite sides of the diaphragms under control of the control valve assembly. The power wall is connected to move the master cylinder input means which actuates both primary pistons, and is so arranged as to permit movement of the other master cylinder input means without requiring movement of the power wall when no booster assist force is available.

United States Patent 1 Nordeen' 11] 3,766,736 Oct. 23, 1973 [75] Inventor: Donald L. Nordeen, East Lansing,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: May 31, 1972 [21] Appl. No.: 258,250

[52] US. Cl 60/550, 60/553, 91/391 R [51] Int. Cl. Fl5b 7/08, Fb 13/10 [58] Field of Search /545 P, 54.6 'P,

[56] References Cited UNITED STATES PATENTS 3,559,406 2/1971 Gardner 60/545 P 3,422,622 1/1969 Arentoft et a1 60/54.6 P

3,473,329 10/1969 Eggstein 60/54.6 P

3,162,018 12/1969 Daley 6.0/54.6 P,

3,540,219 11/1970 'Huruta et al. 60/54.6 P

Primary ExaminerMartin P; Schwadron Assistant Examiner-A. M. Zupcic Attorney-W. E. Finken et al.

[57] ABSTRACT A master cylinder assembly has a secondary piston assembly and a primary piston assembly mounted in a common bore to provide a primary pressurizing chamber between the piston assemblies and a secondary primary chamber between the secondary piston assembly and one end of the bore. The primary piston assembly is composed of two concentric pistons, one extending through a bore in the other. Two input members are provided, one of which is arranged to move both primary pistons concentrically under brake booster'power to actuate the master cylinder, and the other of which is arranged to move only one of the primary pistons, without moving the other, to actuate the master-cylinder manually when no power assist is available from the booster. The booster assembly is actuated through a manuallymoved push rod which in turn permits movement of a valve input member forming a part of the booster control valve assembly, The valve input member is arranged so that it normally follows movement of the push rod but is not positively attached thereto. A reaction system in the booster provides for booster feel to be transmitted to the input push rod. The booster control valve assembly is mounted in the booster power wall. The power wall includes one or more power diaphragms and is actuated by differential pressures imposed on opposite,

sides of the diaphragms under control of the control valve assembly. The power wall is connected to move 1 Claim, 2 Drawing Figures 58 32. 22 5 a as i; ate. at: a ,30 72' MASTER CYLINDER FOR POWER AND NO-POWER ACTUATION It is common to provide a brake system with a master cylinder having manual pressurizing chambers so that the brake system is divided into two or more fluidly independent brake pressurizing circuits. It is also common to actuate such master cylinders through a power brake booster in order to maintain high level of brake pressurization without requiring high levels of brake pedal pressure or pedal movement under normal operating conditions. The brake booster may be powered pneumatically or hydraulically, it being most common at this time to use a vacuum-atmospheric brake booster in automotive vehicles. In some instances, particularly in trucks, an atmospheric-super-atmospheric air pressure system is used, and in other instances, a hydraulically pressure actuated system is used. In all of these arrangements, an outside power source is depended upon to obtain the power assisting action of the brake booster. The booster can at times have insufficient outside power supplied to it so as to reduce or eliminate the power assist available. While brake boosters in master cylinder assemblies can also be normally actuated manually, there will of necessity be reduced brake effectiveness since less total force is available to actuate the master cylinder.

Different arrangements and proposals are known which will tend to improve the brake effectiveness under such circumstances. It is desirable to accomplish this insofar as possible without requiring a change in the normal brake pedal height, and the normal operation of, the brake system should not be materially affected. The manually operated system should be utilized any time there is insufficient power assist and, at the same time, the normal braking operation should not be affected. In order to obtain these goals, and to provide a reasonable brake system with reduced or nopower assist, the braking system is designed so that normal stops can bemade with reasonable pedal'force exerted by the vehicle operator.

- In the preferred embodiment 'herein disclosed and utilizing the invention to which the claims are directed, increased brake effectiveness is obtained by changing the mechanical advantage between the brake pedal and the master cylinder hydraulic pressure by providing two primary pistons in the master cylinder, and by providing a power brake booster which is arranged to normally actuate both primary pistons. However, if a loss of power assistance occurs, the booster is arranged to actuate only one of the primary pistons. This has the effect of changing the brake pedal ratio when power assist is not available and results in a greater hydraulic pressure output per unit of brake pedal apply force. The brake booster is also arranged to apply the brake pedal force through the brake pedal push rod directly to the master cylinder so that the booster power wall does not have to be displaced. The invention herein claimed is directed to the master cylinder portion of the booster and master cylinder assembly.

IN THE DRAWINGQ FIG. 1 is a cross section view of a brake booster and master cylinder assembly embodying the invention.

FIG. 2 is a cross section view of a portion of the master cylinder assembly of FIG. 1, taken in the direction of arrows 2-2 of that FIGURE.

The brake booster and master cylinder assembly 10 includes a boosterassembly 12 and a master cylinder assembly 14. The booster assembly is illustrated as being a vacuum suspended-type booster similar to those currently used in production automobiles. It has a housing 16 provided with a rear wall 18, a front wall 20 and an intermediate wall 22. Power wall means 24 is contained within the booster housing 16 and includes the power piston 26 and diaphragms 28 and 30. The inner peripheries of the diaphragms are sealingly con- .nected to the powerpiston 26 and to the housing 16,

with the diaphragms being positioned in the housing on opposite sides of intermediate wall 22. The housing walls and diaphragms therefore divide the housing into chambers 32, 34, 36and 38. Chambers 34 and 38 are interconnected and normally impressed with vacuum from a suitable vacuum source, as is well known in the art. When the booster is in the released position, chambers 32 and 36 are also impressed with vacuum. When the booster is actuated, as described below, atmospheric pressure is controllably admitted to chambers 32 and 36, causing the diaphragms and power piston to move leftwardly, as seen in FIG. 1, to actuate master cylinder assembly 14.

The power piston 26 has a rearwardly extending section 40 which extends outof the housing wall 18 and may be suitably covered by a boot 42. Section 40 has v the booster control valve assembly 44 received therein. This valve assembly includes the vacuum valve seat 46, which is annularly formed as a part of piston 26, the valve member 48 mounted in section 40 for axial reciprocal movement relative toseat 46 and urged toward that seat by spring 50, and the valve input member 52. This input member is'reciprocably mounted concentrically within the valve seat 46 and is formed to provide the air valveseat 54. This general arrangement is well known in the art and the manner of operation is likewise so well known as to only require a general description. In the normal released position, valve seat 54 engages valve member 48 and holds it away from valve seat 46 so that vacuum is supplied to all of the booster chambers 32, 34, 36 and 38. When the valve input member ismoved leftwardly, valve member 48 follows until it engages vacuum valve seat 46, thus closing the vacuum connection to chambers 32 and 36. Further movement of the valve input member 52 moves valve seat 54 away from valve member 48, admitting air under atmospheric pressure to chambers 32 and 36. The pressure differentials acting on diaphragms 2 8 and 30 and on piston 26 cause the power wall assembly to move leftwardly against the booster piston return 7 spring 56. Since the valve seat 46 and the valve member 48 are mounted in the piston section 40, they also move'leflwardly relativeto the valve input member 52.

relative to piston 26, removing valve member 48 from the vacuum valve seat 46, therebyde creasing the pressure differential across diaphragms 28 and 30 and permitting rightward movement of the power wall means under the force of booster return spring 56. To this extent, the booster operates in the same manner as boosters currently used.

The booster valve input member 52 is engaged by an annular spring retainer 58 on its rightward end, the spring retainer being concentrically within and spaced from the valve member 48. The spring retainer is formed at the end opposite the valve input member 52 to provide a spring seat'60. Another spring seat 62, which may be a snap ring, is provided in the outer end of piston section and a compression spring 64 is seated on seats 60 and 62 so as to urge spring retainer 58 leftwardly. Since the leftward end of the spring retainer 58 engages valve input member 52, the valve input member is also urged leftwardly. It is provided with a snap ring on another stop member 66 which can engage one side of shoulder on piston 26 to limit its leftward movement relative to piston 26. Valve input member 52 is provided with another snap ring or stop member 68 on the opposite side of the piston shoulder 70, so as to limit rightward movement of the valve input member relative to the piston 26. Thus, shoulder 70 is positioned between snap rings 66 and 68 and limits valve imput movement beyond a predetermined amount.

The push rod 7 is suitably connected atone end, not shown, to the brake pedal so as to be movable leftwardly under brake pedal actuating force exerted manually by the vehicle operator. The other end of push rod 72 is suitably connected, as by a ball and socket pivot joint, to a force transmission member 74. Member 74 is reciprocably received in a bore 76 formed in through from a shoulder 100 of member 74. Extension 98 has a spring seat 102 mounted on its leftward end within cup 96 and supporting the right end of compression spring 104. A piston-like output member 106 is reciprocably received within the cylinder wall 88 and the tively connected through compensation ports 122 and 124 with bore 126. The right or rear end 128 of housing 116 is suitably secured to the wall 20 of the brake booster assembly and the open end of the bore 126 extending through end 128 is aligned to receive the master cylinder input members formed by left end 92 of piston 26. The right end of member 74 adjacent the ball and socket joint has a shoulder 78 which mates with a shoulder 80 formed interiorly of the valve input mem-.

ber 52. The valve inputmember is generally annular in form so that the push rod 72 and the member 74 extend therethrough. Other than the abutting engagement of shoulder 78 and 80, there is no direct mechanical force -and.piston shoulder 70, by theforce'of spring 64 acting on the valve input member through spring retainer 58. Thus, the valve input member 52 will follow the manual input movements of the push rod 72 to control the brake booster.

The leftward end of piston bore 76 has an enlarged section 82 joinging the other portion of the bore at shoulder 84. A power force transmission output member 86 is'reciprocably received within bore section 82 and is generally tubular in form so as to have a cylinder wall 88 interiorlythereof. The right end 90 of output member 86 is engageable with shoulder 84 for tramsisssion of brake booster generated force in a leftward direction. The left end 92 of output member 86 forms a master cylinder input member and is arranged to actuate the master cylinder assembly 14 in a manner to be described. A reaction disc 94, suitably formed of a rubber-like material,.is received within the cylinder wall 88 of member 86 adjacent output member end 90 so that its outer periphery engages the cylinder wall 88, one side engages shoulder 84, and the other side is engaged by a movable cup 96 which is reciprocably mounted within the cylinder wall 88. The disc 94 and cup 96 are axially apertured so that a reduced diameter extension 98 of the force transmission member 74 extends theremember 86 and the bifurcated member 110. A secondarypressurizing piston assembly is-reciprocably received in the forward end of bore 126 and is normally axially spaced from the bore end 132 to form within the bore the secondary pressurizing chamber 134. Aprimary pressurizing piston assembly 136 is reciprocably received in the rear end of bore 126 in axial alignment with piston assembly 130 and is normally spaced from piston assembly 130 to form the primary pressurizing chamber 138 in the bore between the two piston assemblies. A piston stop in the form of snap ring 140 is inserted in the rear end of the bore 126 to provide a rearward stop for piston assembly 136. Piston return springs 142 and 144 are respectively positioned in chambers 134 and 138 and, as will be further described, cooperate to hold piston assembly 136 in abutting relation with stop 140 when the master cylinder is not actuated and thereby precisely position both piston assemblies so that compensation port 122 is open to chamber 138 and compensation port 124 is open to chamber 134. r 3

Pistoh assembly 130 includes a piston 146, which is generally spool-shaped The forward piston land 148 has a piston cup150 engaging the forward end thereof and also acting as a valve-to close compensation port 124'when the piston is movedv in the pressurizing direction. An axially positioned piston extension 152 extends forwardly of land 148 and the extension end 154 is aligned for engagement with bore end 132 after a predetermined amount of forward movement of the piston. A- spring seatl56 is mounted on extension 152 and receives one end of piston return spring 142. The other end of spring142 engages bore end 132.'The rear land 158 of piston l46'hasoppositely, directed V-bloclt seals 160 and 162 thereon which effectively seal the chambers on both sides of land 158. A rearwardly ex tending boss 164 is provided on the rear face of land 158 and is sufficiently smaller in diameter to permit the spring retainer 166 to have its annular forward end 167 engage the annular surface of land 158. The retainer forward end 167 is flanged to provide a seat for the forward end of piston return spring 144. The forward end 167 of retainer 166 is pressed against the annular surface of land 158 but is not otherwise connected thereto to permit leftward movement of the secondary piston 146 without a corresponding movement of said retainer 166. The retainer 166 and spring 144 are considered to be parts of the primary piston assembly 136, and are located in chamber 138.

Piston assembly 136 includes a first primary piston 168, which is generally spool-sahped and provided with a front land 170 and a rear land 172. Cup-like seals 174 and 176 are respectively provided on lands 170 and 172 to seal with the bore 126. Piston 168 has a bore 178 extending axially therethrough so as to reciprocably receive the second primary piston 180. Thus the two primary pistons are concentrically mounted. A sea] 182 is provided between the two pistons to seal bore 178.

The rear end 184 of piston 180 extends out of bore 178 past the first primary piston rear land 172 and has secured thereto a plate member 186. The plate member is of substantially the same diameter as piston land 172 and is axially positioned between that land and piston stop 140. The plate member is apertured or otherwise suitably formed to provide axially extending openings therethrough which are positioned radially outward of the end 184 of piston 180 so that the apertures are in axial alignment with at least portions of the rear face 188 of land 17 2. In the particular construction shown in the drawing, plate member 186 is shaped somewhat like a butterfly or-bow tie, as seen in FIG. 2. The apertures in this instance are formed at 190 and 192 by the arcuately omitted portions of the plate through member 86, it passes'through plate member.

186 to both pistons 168 and 180, moving them concurrently in a forward direction away from stop 140. However, if brake actuating force is transmitted only through the bifurcated member 110, only piston 168 is moved forwardly, leaving plate member 186 in position against stop 140 and affording no movement of piston The forward end 196 of piston 180 has a stop 198' thereon in the form of a snap ring, the piston end and snap ring being located in chamber 138. The rear end 200 of spring retainer 166 is received over snap ring 198 and inwardly flanged to normally rest against the snap ring whenthe master cylinder is in the'released position. Thus, spring 144 is caged betweenspring seat 167 and the forward face of piston land 170, which provides a spring seat for the rear end of spring 144. The inwardly flanged end 200 of spring retainer 166 is slidably mounted relative to piston 180 so that some relative movement can occur. Under certain conditions of operation, such as when the master cylinder is actuated but no pressure is generated in chamber 138, piston 168 can move forwardly against'spring ,144 until the forward face of the piston engages the spring retainer end 200. This will result in a mechanical force transmitting connection through abutting surfaces to move piston assembly 130 forwardly even though no pressure is generated in chamber 138. If this occurs under power boost actuation, piston 180 will move with piston 168.

In normal brake operation, with the primary pressurizing chamber 138 connected to one brake circuit and the secondary pressurizing chamber 134 connected totransmitting member 74 will engage the inner portion of reaction disc 94 and shoulder 84 of the power piston 26 will engage the outer-portion of the reaction disc and the rear end of member 86. The power brake apply force which moves piston 26 leftwardly is transmitted primarily through member 86 to move both primary pistons 168 and 180 in the forward, fluid pressurizing, direction. Some of the power apply force is also transmitted through reaction disc 94 and cup 96 to output member 106 and bifurcated member 110 to exert some power generated force directly on piston 168. Reaction to this force will be returned through the reaction disc and a portion thereof exerted through the innerportion of disc 94 against force transmission member 74 to the push rod 72 to provide feel to the brake pedal. With both primary pistons moving leftwardly, force is also transmitted through spring144 to move piston assembly leftwardly. Cups and 174 respectively ,cover compensation ports 122 and 124, and further leftward movement pressurizes fluid in chambers134 and. 138, actuating the brakes.

If a the brakes are applied and no booster power is available, initial leftward movement of force transmission member 74 by push rod 72 will cause the valveassembly 44 to operate as before. However, with no pressure differential imposed thereon, the power wall of the booster will not be moved against the return spring 56.

Piston 26 will not be axially moved and, therefore,

member 86 will not be axially moved. Since movement of member 86 is necessary to move plate member 186 and piston 180, those elements will not be moved axially. However, the manually exerted force transmitted through member 74 willpass through reaction disc 94 after shoulder 100 engages it-,and cup 96;will be moved leftwardly. This will in turn move member 106 leftwardly, causing the bifurcated master cylinder. input member 110 to be moved leftwardly. Since the bifurcated ends only engage piston 168,-this leftward movement will result in movement only of primary piston 168, closing compensation port 22 andfthen commencing to pressurize fluid in chamber 138.

Since the effectivearea of the primary piston assembly is now smaller, a greater hydraulic pressure for a given input force will result. While this pressure will be lower in terms of brake pedal stroke, it will'be greater than would be the case if the primary piston assembly had the same effective area at all times. This relatively high hydraulic pressurewill be generated in both presfrom the end 167 of retainer 166 in response to increased pressurization of fluid within" the pressurizing chamber 138. The booster piston return spring 56 need not be manually overcome. it is for this reason that the valve input member 52 is not mechanically fastenedto the push rod 72 or member 74. As'can be seen, the arrangement permits the push rod 72 to manually move member 74 away from the valve input member, separating shoulders 78 and 80, after snap ring 66 engages shoulder 70. This will also occur upon booster run-out when there is insufficient pressure differential to fully actuate the assembly.

Since there is no secured connection between the booster input and the valve, the preload forces on the various springs in the system must be carefully controlled to insure proper operation. The booster return spring is required so that the booster is fully returned when the brakes are not applied. Piston return spring 142 acts through the piston assemblies, including spring 144, and then through the booster output members and the force transmission member'74 to move valve input member 52 rightwardly against the force of spring 64 and to also move the push rod 72 to the brake release position. In order to accomplish this, and to insure the proper relationship between the master cylinder piston assemblies, the preload on spring 144 must be greater than the force from spring 142. Spring 104 also acts to insure the full return of valve input member 52 and valve 48. Therefore, the preload force on spring 104 is greater than the preload force on spring 64 but is less than the preload force of spring 142. Springs 64 and 104 insure direct mechanical contact between transmission member shoulder 78 and valve input member shoulder 80 unless there is a loss of brake booster power. There is also sufficient clearance provided between the booster piston 26 and the member 86 so that the displacement required in the reaction disc 94 to balance the booster valve can be obtained for all power operating conditions. The area ratio between primary pistons 168 and 180 is selected so that the change in pedal displacement in the event of loss of booster power is within an acceptable range. At the same time, there must be sufficient difference in the areas of these pistons to achieve the desired amount of reduced pedal effort under this circumstance.

I claim:

1. A master cylinder assembly adapted for manual and power operation and comprising:

a housing having a bore and brake fluid reservoir means and compensation port means interconnecting said bore and said reservoir means;

a primary piston assembly adjacent one end of said housing and a secondary piston assembly reciprocably received in said housing bore in axially spaced relation and defining with said bore a pri-v mary pressurizing chamber between said piston assemblies and a secondary pressurizing chamber between said secondary piston assembly and the other end of said housing bore;

said primary piston assembly including a first primary piston having a bore therethrough and a second primary piston reciprocably received through said piston bore, first stop means on one end of said second primary piston and normally axially engaging the one end of said first primary piston further away from said secondary piston assembly, second stop means on the other end of said second primary piston, said second stop means being normally axially spaced from the other end of said first primary piston and from the adjacent end of said secondary piston assembly, spring retainer means in said primary pressurizing chamber and having one end reciprocably mounted on said second primary piston intermediate and engageable with said second stop means and said other end of said first primary piston and having the other end engaging said adjacent end of said secondary piston assembly, and a first spring caged axially between said spring retainer means and said other end of said first primary piston in said primary pressurizingchamber with a predetermined preload, the first spring preload urging said spring retainer means one end against said second stop means and said first primary piston one end against said first stop means;

a second spring in said secondary pressurizing chamber operatively acting on said housing bore other end and said secondary piston assembly and having a lesser preload than said first spring; third stop means in the one end of said housing bore and normally engaged by said first stop means when the master cylinder is not actuated; first force input means for said primary piston assembly engaging said first stop means and adapted to be power operated to move said first and second primary pistons concurrently in the fluid pressurization direction, and second force input means engaged with said first primary piston one end and bypassing said first stop means and adapted to be manually operated independently of said first force input means to move said first primary piston in the fluid pressurising direction independently of said second primary piston. t i l i 

1. A master cylinder assembly adapted for manual and power operation and comprising: a housing having a bore and brake fluid reservoir means and compensation port means interconnecting said bore and said reservoir means; a primary piston assembly adjacent one end of said housing and a secondary piston assembly reciprocably received in said housing bore in axially spaced relation and defining with said bore a primary pressurizing chamber between said piston assemblies and a secondary pressurizing chamber between said secondary piston assembly and the other end of said housing bore; said primary piston assembly including a first primary piston having a bore therethrough and a second primary piston reciprocably received through said piston bore, first stop means on one end of said second primary piston and normally axially engaging the one end of said first primary piston further away from said secondary piston assembly, second stop means on the other end of said second primary piston, said second stop means being normally axially spaced from the other end of said first primary piston and from the adjacent end of said secondary piston assembly, spring retainer means in said primary pressurizing chamber and having one end reciprocably mounted on said second primary piston intermediate and engageable with said second stop means and said other end of said first primary piston and having the other end engaging said adjacent end of said secondary piston assembly, and a first spring caged axially between said spring retainer means and said other end of said first primary piston in said primary pressurizing chamber with a predetermined preload, the first spring preload urging said spring retainer means one end against said second stop means and said first primary piston one end against said first stop means; a second spring in said secondary pressurizing chamber operatively acting on said housing bore other end and said secondary piston assembly and having a lesser preload than said first spring; third stop means in the one end of said housing bore and normally engaged by said first stop means when the master cylinder is not actuated; first force input means for said primary piston assembly engaging said first stop means and adapted to be power operated to move said first and second primary pistons concurrently in the fluid pressurization direction, and second force input means engaged with said first primary piston one end and bypassing said first stop means and adapted to be manually operated independently of said first force input means to move said first primary piston in the fluid pressurizing direction independently of said second primary piston. 